1. Field of the Invention
The present invention relates to colored pigments, particularly magnetic pigments, to processes for their preparation, and to various end applications thereof, notably in the production of developing powders.
2. Description of the Prior Art
It is well known to this art, for numerous applications, to add mineral charges to a wide variety of different materials for purposes of imparting any given number of particular properties thereto. Among the most widely encountered such properties are optical, mechanical and rheological properties. In particular, in the production of developing powders, magnetic pigments constitute a basic element thereof.
For certain applications, it is necessary to incorporate charges in combination with a pigment or dye. In general, these charge/pigment compositions are produced by physically admixing the mineral charge with the dye. However, such process suffers from a number of disadvantages.
A first disadvantage is that it is difficult for a given mineral charge to contain all of the desired coloration. This disadvantage is particularly significant when preparing magnetic pigments for developing powders. Thus, the magnetic particles are based on iron or ferrites, which are very dark colors and which cannot be totally masked by dyes. It is therefore essentially impossible to produce developing powders having a very bright color.
Another disadvantage is linked to the compatibility of the dye with the material intended to be provided with the pigmentation. Consequently, for a given material and as a function of said compatibility, it will only be possible to use a limited number of dyes. In this connection it is also necessary to take account of the dispersibility of said dye in the same material.
Moreover, the resulting colored compositions can display a low resistance to chemical or photochemical deterioration, as well as to abrasion.